PETROLEUM-SOAP EMULSIONS. 299 



emulsion made with 1 part of thick milk of lime from fat lime and 

 5-30 parts of petroleum. This emulsion is more stable than that made 

 with water, but less so, however, than that made with soap solution. 

 It was especially intended to be added to arsenical bouillies to increase 

 their insecticidal value. 



4. Pi'troleuin Emulsion ivith Salt Water. — This emulsion is more 

 difficult to make than that made with pure water, owing to the greater 

 difference between the densities of the two products. It is frequently 

 used in Switzerland, owing to its precious properties against the woolly 

 aphis : 8 lb. of petroleum are emulsified w^ith 2 lb. of a 25 per cent 

 solution of common salt. 



5. Petroleum Emulsion and Soap Solutioyi. — Petroleum gives with 

 soapy solutions very stable emulsions. All soaps do not lend them- 

 selves thereto equally well. The soap ivhich gives the most perfect 

 emulsion is made in America from lohale oil. These emulsions keep 

 a very long time whilst those made with other soaps become curdy in 

 a few days. To increase the stability of emulsions made from ordinary 

 soaps, alcohol or carbonate of soda is added. Concentrated stable 

 emulsions are prepared with the appearance of a cream which are 

 suitably diluted at the moment of use. A good preparation should be 

 capable of being diluted to a certain extent without drops of petroleum 

 forming on the surface of the liquid. 



Example. — 2^ lb. of soap are cut into thin slices and dissolved in 

 1 gallon of boiling water. After drawing the fire there is added slowly 

 with constant stirring 10 gallons of petroleum at 18°-20° C. ; petroleum 

 only emulsifies with difficulty below this temperature. To obtain a 

 perfect emulsion it is necessary on the large scale to stir with a 

 mechanical agitator, on the small scale with an ordinary spraying 

 machine drawing in the mixture and expelling it repeatedly. The 

 emulsion is more perfect if another gallon of boiUng water be added 

 and the whole mixed once more. Rain water or distilled water should 

 be used, or the hard water available corrected by carbonate of soda. 

 Very different mixtures have been recommended ; the following are the 

 principal ones : — 



TABLE LIX. — Showifig the Ingredie?its of Several Petroletim Emuhlons. 



These emulsions are comparatively stable, less so, however, than those 

 now made with rvhale oil and intended to be kept. They are thinned 

 when about to be used in such a way that the emulsion only contains. 

 2-5-6 per cent of petroleum, quantities which, according to Fleischer 



